Hogwarts is built in a valley area — surrounding mountains are part of the landscape — with the fairly large Black Lake to the south of the main building. The huge main oak front doors leading into the Entrance Hall face the west, and open up to sloping lawns. The deep Forbidden Forest extends around to the west of the Castle. There are also exterior greenhouses and vegetable patches on the school grounds.

It was the setting of the final battle of the Second Wizarding War, the Battle of Hogwarts, which saw members of Order of the Phoenix, Remus Lupin, Nymphadora Tonks, Fred Weasley, Colin Creevey, Lavender Brown and Severus Snape die. The castle was severely damaged, but ultimately the Order of the Phoenix won, when Harry Potter defeated his evil nemesis, Lord Voldemort in the Great Hall.

Contents

Magic

The castle is supported by magic (unable to be maintained or constructed by any other means)[1], a good example being the moving staircases, a feature contributed by one of the four Hogwarts founders, Rowena Ravenclaw.

Hogwarts is also protected by numerous ancient spells and incantations, such as the Anti-Disapparition Jinx. It is also unplottable and has been bewitched so that, if Muggles approach the castle, all they will see is a mouldering ruin with a sign warning them to keep out and that it is unsafe. The protective magic over Hogwarts is not only strong enough to apparently resist the dispelling effects of the Taboo but also to repel even talented dark wizards.

As a result of all the magic that occurs on premises (both from learning students, magical artefacts therein and the enchantments cast over the building itself) a magical atmosphere pervades the entire structure, causing any technology that is not adapted to run off of it (like Colin Creevey's camera) to fail.

Below Ground Floor

Chamber of Secrets

"He was standing at the end of a long, dimly lit chamber. Towering stone pillars entwined with more serpents, rose to a ceiling lost in darkness, casting long, black shadows through the odd, greenish gloom that filled the place."

The Chamber of Secrets was allegedly created deep under the dungeons of Hogwarts Castle during the Medieval times by Salazar Slytherin, who disagreed with the other Hogwarts Founders on the merits of blood purity. The Chamber of Secrets was home to an ancient Basilisk, which was intended to be used to purge the school of Muggle-born students. The entrance can be found in Moaning Myrtle'sbathroom on the second floor. In order to gain entrance one must say "open" in Parseltongue and a sink will open into a slide. While falling down the large, dark pipe, one can see hundreds of other pipes leading off. At the end of the pipe, one is launched into a damp, stone chamber. This room is stated to be "miles beneath the school and under the Black Lake". This is where Tom Marvolo Riddle used his ability to speak parseltongue and attack Harry Potter.

Potions Classroom

The Potions Classroom is where Potions classes are taught. The classroom used to be squared-sized, very large, with large tables and windows[2]. From 1995-1996, the classroom was an oval shape and relatively smaller, with small work tables[3]. In 1996, the classroom was extended, adding space for more work tables[4].

Head of Slytherin's Office

This office was used by Severus Snape during his long tenure as Potions master at Hogwarts. It was a gloomy and dimly-lit room found in the school Dungeons. The shadowy walls were lined with shelves of large glass jars filled with slimy, revolting things, such as bits of animals and plants, floating in potions of varying colours[5]. The office had a fireplace. In a corner, there was a cupboard containing Snape's private stock of potion ingredients. The office is sealed with a spell only wizards can break[6].

Slytherin Common Room

The Slytherin Dungeon is located behind a wall in the dungeons of Hogwarts. A Password spoken to the wall is required to enter it; whereupon a passage is revealed leading to the Common room -- a low-ceilinged, dungeon-like room with greenish lamps and chairs. This dungeon extends partway under the lake. Off of this room also includes the Slytherin Boys Dormitory.

Basement

Hufflepuff Common Room

"It is a very cosy and welcoming place, as dissimilar as possible from Snape’s dungeon. Lots of yellow hangings, and fat armchairs, and little underground tunnels leading to the dormitories, all of which have perfectly round doors, like barrel tops"

The Hufflepuff Basement is the common room for Hufflepuff students at Hogwarts. The entrance to the Hufflepuff Basement is hidden behind a stack of barrels. It can be entered by tapping a certain rhythm on the barrels. It is located near the kitchens. The cellar is decorated with yellow hangings and filled with fat armchairs. Underground tunnels lead off to the students' dormitories and all the doors are perfectly circular, like barrel tops. This is the only common room Harry Potter does not enter at some point during his years at Hogwarts.

Kitchens

The Hogwarts kitchen is located directly under the Great Hall, down the same staircase that leads to the Hufflepuff Common Room. It contains tables identical to those in the Great Hall and are directly below them; food must simply be placed on the tables in the kitchens, and it magically appears in the Great Hall. The kitchens are staffed by over 100 house-elves including Dobby, Winky, and Kreacher (after Harry Potter inherited him and ordered him there in 1996). To gain access to the kitchens, one must tickle the pear on a fruit portrait, which then turns into a door knob.

Great Hall

The Great Hall in Hogwarts is the main gathering area in the school. Students eat their meals, receive daily owlposts, and have certain special events. The Great Hall is a large hall that can easily hold all of the school's students, staff and guests. It has tall walls that reach up to the ceiling, which is enchanted to look like the sky above. It was the scene of Harry Potter and Lord Voldemort's final showdown, which was the Dark Lord's ultimate defeat. This was because the Elder Wand refuse to kill its true master, so Harry was not killed. Since Voldemort was now a mortal man, the curse rebounded on him, killing Tom Marvolo Riddle once and for all.

Caretaker's Office

The caretaker's office is the room where Argus Filch lived in Hogwarts Castle. It is connected to the Entrance Hall, on the Ground Floor of Hogwarts Castle. It is a small, simple, windowless room with a single oil lamp in the ceiling. It smells vaguely of fried fish.

Transfiguration Courtyard

This is one of the cloisters in the inner part of Hogwarts Castle. This courtyard has grass in the open area, in which a big tree has grown over the centuries. There is one massive iron Armillary Sphere that stands in the centre of the courtyard.

Transfiguration department

This is a wing at Hogwarts Castle containing the rooms dedicated to the teaching of Transfiguration. The Transfiguration department is presumably located around the Middle Courtyard area, including such rooms as Classroom 1B.

Transfiguration Classroom

This classroom is where Transfiguration class is taught. The classroom is located on the ground floor around the Middle Courtyard. The classroom itself is big, surrounded by high windows, has four rows of three desks, and still has enough room for several cages and bookshelves, two chalkboards, and a desk.

Viaduct

This viaduct is constructed of stone, and extends all the way down to the lake. It is connected to the Viaduct Courtyard at one end and is connected to the left long viaduct tower and the right long viaduct tower.

Grand Staircase

The Grand Staircase is a massive structure in Hogwarts Castle, mainly used to access each floor of the castle, including the dungeons. There are hundreds of Portraits covering the walls in this tower, some of which conceal secret passages to other areas within the school. The multiple staircases in the Grand Staircase lead from platform to platform and go as high as the seventh floor where they come to an end.

Muggle Studies Classroom

Hospital Wing

The Hospital wing was run by Poppy Pomfrey. Students who suffer mishaps during the school year are sent or brought to the hospital wing for treatment. The hospital wing is well equipped to deal with all manner of magical and mundane injuries, from broken limbs to regrowing lost bones. Only in the most severe cases are students sent to St. Mungo's Hospital for Magical Maladies and Injuries for further treatment, such as when Katie Bell touched a cursed Opal necklace in 1996.

Matron's Office

This office is a large room adjacent to the Hospital wing at Hogwarts Castle owned by Poppy Pomfrey, the matron. It contains a bookcase, a desk, two closets, two beds for patients, and another bed closed off from the room by a curtain.

Tapestry Corridor

This corridor located on the first floor of Hogwarts Castle. It connects the Viaduct Entrance to the main first floor. Its walls are covered in tapestries and, hung over the tapestries, portraits of wizards.

Storeroom

This storeroom is located in the Tapestry Corridor, this was where Severus Snape stored his private supply of potions and potion ingredients. It was one of two known potions' store rooms in the castle; this being his private store; the other being the student store cupboard. The students cupboard is located in the dungeons. Items stored in Snape's store room included Veritaserum and ingredients for Polyjuice Potion.

Girl's Lavatory - Out of Order

This girls' lavatory (also known as Moaning Myrtle's bathroom) is situated on the first floor of Hogwarts Castle. It has been out of order ever since a student named Myrtle was killed there by Salazar Slytherin's Basilisk on the orders of Tom Riddle, the Heir of Slytherin. Myrtle has haunted the bathroom ever since, leading it to be a place most students do not want to enter. This bathroom holds the entrance to the Chamber of Secrets.

The Quad battlements

There were battlements all around the top of The Quad at Hogwarts Castle.

These battlements were used by the Hogwarts defence during the Battle of Hogwarts. They were heavily damaged during the course of the battle, with parts of the floor falling in, revealing the corridors below.

Charms Classroom

This classroom is where Charms classes are taught at Hogwarts School of Witchcraft and Wizardry. The classroom has four long, large desks that are built like stairs, and are located on both sides of the classroom. There is also a large fireplace in the room, as well as several stacks of books, where Professor Flitwick lectured his pupils.

Clock Tower Entrance

This is one of the three main entrances of Hogwarts Castle. It consists of a large open space at the base of the Clock Tower with two stairwells going up towards the upper levels of the tower. Opposite the main entry there is a large window. A portrait of Damara Dodderidge was hung here and, in 1995, so was a portrait of Termeritus Shanks. The massive pendulum of the Clock swings over this entrance. The entrance can be sealed with a portcullis (which can be lowered and raised with the aid of a lever) and the massive double doors can be locked with numerous bolts.

Defence Against the Dark Arts Classroom

This classroom is where Defence Against the Dark Arts class is taught. It is located on the third floor. Although in 1991, ProfessorQuirinus Quirrell taught in a different classroom because the third floor was out of bounds. An iron chandelier hung from the ceiling, as well as a Dragon's skeleton. On one end of the classroom stands a projector that is activated by magic. Several desks and tables can be found in the classroom as well as some sets of large windows. The classroom decoration had several changes over the years, spanning from lots of pictures of Gilderoy Lockhart to tons of skeletons and Shrunken Heads.

Library

The Library is located on the third and fourth floors of Hogwarts School of Witchcraft and Wizardry and contains tens of thousands of books on thousands of shelves. Overseen by Madam Irma Pince, the library is where students can go to peruse or borrow books to supplement their studies (or for personal enjoyment). The library closes at 8 pm.

Other locations on the third floor

Fourth Floor

Restricted Section

The Restricted Section is an area in fourth floor section of the Hogwarts Library closed off by a rope and only accessible to students with permission from a professor. In order to enter, they must present a signed note from a professor. The books within the Restricted Section typically discuss the Dark Arts or other information not for the general public or young children. They may be studied by older students for Defence Against the Dark Arts.

Other locations on the fourth floor

Fifth Floor

Prefects' bathroom

This is a special bathroom that is restricted to use by school Prefects, Head Boys, Head Girls and Quidditch captains. It is located on the fifth floor behind the fourth door to the left of a statue of Boris the Bewildered, which only opens when given the correct password, which when mentioned in the fourth book; by Cedric Diggory, is 'Pine Fresh.'

East Wing

This is a large hall located on the sixth floor of Hogwarts Castle. There is a huge fireplace in the center of the room and some portraits hung on the walls. There are various suits of armour, which guard the room after the sun is down. The entrance is located on the Glanmore Peakes' Corridor and it has an entryway to the room Fred and George Weasley hid the Marauder's Map.

North Wing

This wing has hundreds of bookshelves lined along the walls and various tables and furniture placed around the room. It serves the Castle as a reading room and study hall. There are two entrances; one in the seventh floor corridor and the other by the Fat Lady's portrait.

Divination Classroom

This is where Divination classes are taught at Hogwarts. It is located in the North Tower. It is accessible through a circular trapdoor and is described as looking like a cross between somebody's attic and an old-fashioned teashop. The Divination Staircase leads to this classroom.

Other locations on the seventh floor

Towers

Astronomy Tower

Astronomy Tower

The Astronomy Tower is the tallest tower at Hogwarts Castle surrounded by a parapet and turret. It is where students study the stars and planets through their telescopes in Astronomy lessons with ProfessorAurora Sinistra. This is usually done at midnight where the stars are best seen. The tower is usually out-of-bounds except for classes. All the way down from the boathouse you can see the huge window of the Astronomy Tower. Located within this tower is the Astronomy Corridor, Astronomy reading room, Astronomy classroom, Astronomy stairwell, Astronomy department and the Astronomy Room. In 1997, Hogwarts' headmaster, Albus Dumbledore was killed here on this tower by his eventual successor, Severus Snape. However, it was planned between Dumbledore and Snape to spare Draco Malfoy being a murderer and spare the headmaster from a slow painful death. This was because Dumbledore's hand was poisoned by a dangerous curse created by Tom Marvolo Riddle, to protect his Horcrux (Marvolo Gaunt's ring).

Bell Towers

The Bell Towers are two towers that rise over the main entrance to the Herbology Greenhouses. Between the two towers are a set of double wooden doors which lead along the Ground Floor Corridor. Inside the left Bell Tower is Filch's Office.

Clock Tower

The Clock Tower does not begin at the Ground Floor level. Because it is placed on top of a hill, the Tower begins at the Third Floor level. When you enter the Tower, there is a huge space, like an Entrance Hall with flights of wooden stairs at the right and left side. The first landing is at the Fourth Floor level. It is at this landing that are the clock's gears and face. This same corridor connects the Tower to the remaining castle. If you go up another flight of wooden stairs, you will get to another landing, this time at the Fifth Floor level. It is in this landing that are the clock's bells; some massive gold and copper bells. There is another corridor at this landing; like the other, it links the Tower to the main castle.

Dark Tower

The Dark Tower is a small but high tower near the Transfiguration Courtyard at Hogwarts Castle. This tower seems to be used as a prison. It has several prison cells, with the topmost being at the roof. The cells are not, however, charmed or otherwise protected against breaking-in from the outside. It has seven floors.

Grand Staircase Tower

This tower is probably the most prominent and recognisable feature of Hogwarts Castle. The tower is a circular shape and has a cone shaped roof. The Grand Staircase is located here, and at the top of this tower, are three smaller towers which make up the the Headmaster's tower and serve as the Headmaster's office and residence.

Gryffindor Tower

Gryffindor Tower is located behind the portrait of the Fat Lady on the Seventh Floor of Hogwarts Castle. A Password is required to enter it, which is spoken to the portrait. A circular hole is behind the painting, leading to the Common room, which is a circular room where Gryffindor students can relax after a long day of studying. The Common room is full of squashy armchairs, tables, and a bulletin board where school notices, ads, lost posters, etc. can be posted. A window looks out onto the grounds of the school, and a large fireplace dominates one wall.

The Gryffindor dormitories are also located in the Tower, with two doors leading off from the Common room that open to spiral staircases. One of them leads to the girls dormitory, the other to the boys. The stairs to the girls dormitories are enchanted to become a slide if any boy attempts to climb them, but not vice-versa, since it was deemed that girls were more trustworthy than boys.

Headmaster's Tower

The Headmaster's office is located within this tower. To gain entrance, a password must be given to a stone gargoyle, which will move aside at the correct password to reveal a spiral staircase with moving steps. The office is a circular room with windows, decorated with portraits of previous Headmasters including Dilys Derwent and Phineas Nigellus Black. Many magical instruments are kept here, such as the Sorting Hat and the Pensieve.

Hospital Tower

The Hospital Tower has a semi-ovular shape. It is located on one side of The Quad and is at the end of the hospital corridor which connects the Clock Tower to the rest of the castle. On the first floor of the tower is the hospital wing and school matron's office. There is also a staircase that leads to the fourth-floor corridor and, by extension, to the Grand Staircase.

North Tower

The North Tower is one of the many towers in the castle. The tower is the location for Divination classes and the Divination teacher's office. The entrance consists of a ladder leading through a trap door.

Ravenclaw Tower

The Ravenclaw Tower is located on the west side of Hogwarts, the staircase leading up to the common room is presumably located on the fifth floor, and is the location of the Ravenclaw common room and dormitories. The entrance to the room is at the top of a spiral staircase, and is a door without doorknob or keyhole but a bronze knocker in the shape of an eagle. In order to enter the room, you must answer a question asked by the eagle knocker; if you answer wrong, you must wait for someone who gets it right.

West Tower

The Owlery is located on the top of this tower. During the winter months, the tower is very cold, to the point that one has to be careful with ice on the higher landings. A tightly spiraling staircase leads from the bottom of the tower on the seventh floor up to a door leading out onto the battlements.

The Forbidden Forest

Also known as Dark Forest or Black Forest, the forest borders the edges of the Hogwarts School of Witchcraft and Wizardry grounds. As its name suggests, it is strictly off limits to students - except in the case of detention, or Care of Magical Creatures lessons that occasionally take place there. Of course, with the various dangerous creatures, such as centaurs, Thestrals, unicorns, Hippogriffs and Acromantula living in the Forest, few students would probably even want to venture into it.

Quidditch Pitch

The school has its own Quidditch pitch where each house's Quidditch teams practice and play games against each other. Each year will see a total of six inter-house matches, along with numerous training sessions by each house team.

Quidditch Gate

The Quidditch Gate is the entrance to the Quidditch Pitch. It is flanked by two stone structures which resemble two of the spectator towers surrounding the pitch. Inside the gate, several trophies and shields are housed. Through the gates leads to a steep winding downhill decent from the vicinity of the Covered Bridge.

Entrance Gates

The Entrance Gates to Hogwarts are located a short distance from Hogsmeade Station. The gates would be opened on the first day of term and carriages pulled by Thestrals would take students up to the castle. The Entrance Gates are made of magnificent wrought iron and are flanked by two columns topped with statues of winged boars. Just a few yards from the gates is a small guardhouse with a tall chimney.

Covered Bridge

The Covered Bridge is a feature of Hogwarts Castle. The bridge appears derelict, and is constructed of wood beams which extend to the floor of the ravine it lays across. The roof of the Covered Bridge is sagging and appears thatched and tarred. The bridge blends in with the natural environment surrounding it.

The Covered Bridge begins at one end of the Clock Tower Courtyard, at the base of the Clock Tower. At the end of the covered bridge there is a small stone gazebo with benches. Outside of it is the Stone Circle. Given its unstable look it is possibly held up by magic.

Cauldron cupboard

The Cauldron cupboard is one of the rooms seen on the Marauder's Map. It is possibly a store room where cauldrons are kept. It is possible that the cupboard is close to the Potions Classroom or Snape's provisions cupboard.

When explaining the concept of Legilimency to Harry Potter, Snape said that many ancient spells and charms guard the Hogwarts walls and grounds, ensuring the inhabitants safety.

It's seen that the interiors are not equal to exteriors of Hogwarts. (Ex: Curved walls inside, straight walls outside. Wide inside, narrow outside.) But this is possibly because Hogwarts is supported by magic.

In the Philosopher's Stone film, only the parts of the castle that were needed for the film were created. This means that many areas of Hogwarts were missed.
Areas of the castle included in the film were:

The Prisoner of Azkaban film sees the most drastic changes to the castle in the series. But, the main shape of Hogwarts is still there. These changes probably came about because of the new director, Alfonso Cuarón.
These are some of the main changes that are seen in this film:

Hagrid's Hut is moved down the hill at the back of the castle and a Pumpkin Patch is added.

The Whomping Willow is moved from the Training Grounds to slightly down the hill from the stone circle and off the path toward Hagrid's hut.

Inside the castle there are the following changes:

Dumbledore's Owl Podium makes its first appearance in this film.

The bronze statue of the Hogwarts Architect in the Entrance Hall has been removed (though it returns in the fifth film).

The extra corridor connecting the Entrance Hall to the Grand Staircase has been removed. The Grand Staircase is now directly connected to the Entrance Hall.

The entrance to the Gryffindor Common Room is moved to the Grand Staircase.

The Grand Staircase is made higher, and now has 10 stories.

The furniture in the Gryffindor Common Room has been re-arranged and there are more portraits on the wall in this film than in the others. This is due to a scene which was cut from the final film in which Sir Cadogan moves through the portraits and talks to Professor McGonagall.

In the Great Hall, the raised wooden platform on which the Staff Table sits is modified slightly. A second, higher section is added, allowing for a second table to be placed in front of the existing one. This table appears to be where the people in charge of the Triwizard Tournament sit. The table disappears following this film, but the second raised section remains.

In the Entrance Hall, the door leading into the Chamber of Reception is replaced with two large wooden doors that connect the Entrance Hall to the Viaduct Courtyard.

The cabinets in the Headmaster's Office receive a slight makeover. They now have glass in the doors (as opposed to grilles). Also the Pensieve Cabinet has been added.

While omitted from Harry Potter and the Deathly Hallows: Part 1 aside from a brief cameo appearance, once the film was released, it was shown that although the third film had the highest number of modifications to date, Deathly Hallows: Part 2 has arguably the highest number of changes to prominent features and locations in and around Hogwarts. The noticeable changes to the castle are as follows:

Viaduct Courtyard: It has been enlarged. Also, an archway opposite to the Entrance Hall doors connects it to the Viaduct and the floor has been modified. A short flight of stone steps that lead up to the castle doors has also been added.

The Great Hall is higher and a Hogwarts crest is added to the center of the back window.

The structure connecting the Entrance Hall to the Grand Staircase Tower has been shortened by 1 floor and has two small windows looking out onto the courtyard as opposed to one large one.

It should be noted that the castle shown burning in the teaser poster is actually the look of Hogwarts in Half-Blood Prince.

Most of these modifications were made in order to make the castle more convenient for the battle scene in the film.

Many of these edits to the castle's layout throughout the films can be explained as the effect of the school's ability to change its architecture by magic. However, certain elements, such as the Ravenclaw Tower, can be considered to have always been a part of the castle and simply never seen until the film they are introduced in, and the movement of the Viaduct and the redesign of the Grand Staircase in Deathly Hallows. The grounds around the castle seem to have change great throughout the films too, most notably in Prisoner of Azkaban and Deathly Hallows Part 2.

The Black Lake is also missing, but this is understandable as the lake takes up a great deal of space around the castle that was unavailable to the park. Also, it was required that the castle be easily accessible to visitors.